The present invention relates generally to a transducing device that includes a heating portion.
In a magnetic data storage and retrieval system, a magnetic head typically includes a writer portion for storing magnetically-encoded information on magnetic media and a reader portion for retrieving the magnetically-encoded information from the magnetic media. The reader portion typically includes a bottom shield, a top shield, and a magnetoresistive sensor positioned between the bottom and top shields.
The writer portion typically includes a write pole and one or two return poles (in the case of a perpendicular writer) or a top pole and a bottom pole (in the case of a longitudinal writer). The poles are separated from each other at an air bearing surface (ABS) of the writer by a gap layer, and are connected to each other at a region distal from the ABS by aback gap closer or back via. Positioned between the poles are one or more layers of conductive coils encapsulated by an insulating layer. The writer portion and the reader portion can be arranged in a merged configuration in which layers are shared between the two elements or in a piggy-back configuration in which layers are not shared between the two elements.
To write data to the magnetic media, an electrical current is caused to flow through the conductive coils to thereby induce a magnetic field in the poles. By reversing the direction of the current through the coils, the polarity of the data written to the magnetic media is also reversed.
During operation of the magnetic data storage and retrieval system, the magnetic head is positioned in close proximity to the magnetic media. The distance between the magnetic head and the media is preferably small enough to allow for writing to and reading from the magnetic media with a large areal density, and great enough to prevent contact between the magnetic media and the magnetic head. Performance of the magnetic head depends primarily upon head-media spacing (HMS). Pole-tip recession/protrusion (PTR) at the air bearing surface is considered to be a primary technical gap for meeting required HMS targets. Control of the overall PTR performance is critical in magnetic head designs.
The layers of the magnetic head, which include both metallic and insulating layers, all have mechanical and chemical properties that are different from the substrate. The differences in properties affect several aspects of the magnetic head, including pole-tip protrusion (PTR) of the metallic layers of the magnetic head with respect to the substrate at the ABS of the magnetic head. Two components of PTR exist, thermal pole tip protrusion (TPTR) and current-induced pole tip protrusion (CPTR). TPTR arises from isothermal (global) temperature changes in the magnetic head during drive operation. TPTR is proportional to the difference in coefficients of thermal expansion (ΔCTE) between the magnetic head and substrate materials. Many novel proposals have been made to reduce the TPTR magnitude using low CTE materials, reduced metal material volumes, and compensation schemes.
CPTR results from localized joule heating during application of currents to the writer coil and the resultant heat dissipation into the surrounding components of the magnetic head. CPTR, in contrast to TPTR, is proportional to the first order of the ΔT(CTE) product, where ΔT is the localized temperature rise in the writer core and the CTE is the coefficient of thermal expansion of the insulator material. In principle, CPTR can be reduced by improving thermal conduction away from the coil and the surrounding core structure so that the localized temperature rise is diminished. Replacing the insulator materials with high-thermal conductivity materials is a theoretically straightforward way to optimize the core for thermal dissipation. However, this is difficult due to a processing requirement of filling the coil structure.
To compensate for localized pole tip protrusion, a single-layer heater element is positioned in some magnetic heads either in close proximity to or inside the magnetic writer to heat the magnetic writer to reduce the HMS by controlled thermal expansion. By controlled heating of the writer, thermal expansion of the writer can be controlled to compensate for changes in fly height. One problem with this method is that a significant amount of current must flow through the heater element in order to generate enough heat to effect thermal protrusion.
Additionally, the current path must be designed such that current flowing through the heating element does not form a loop around the magnetic writer and generate a significant magnetic flux. If a significant magnetic flux is generated around the write pole by the heating element, the magnetic flux can result in either inadvertent writing to the magnetic media or inadvertent erasing of data already written to the magnetic media. To ensure that magnetic flux of the remnant write pole is not generated at the write pole, the current flowing in the single-layer heater element must pass along only one side of the via of the magnetic writer.